I have a couple of students with 700+ scores whom I have been giving them the problems toward the ends of the sentence correction and spot the error sections. I went through all the problems in the Blue Book and gave them problems in Barrons. What do I do when I get through Barrons too? Should I use Erica Melzer’s “Grammar Workbook”, or Princeton Review or Kaplan problems? Are there books that have harder problems? Am I going about this the wrong way?